my hemoglobin is too high

I am a 380 time blood donor.   At present, every two weeks I donate double unite of platelets together with a single unit of plasma or, once each 8 weeks, a unit of whole blood.  I take NO medications but MANY supplements.  I believe that none of these supplements contain iron.  The blood bank calls me a 'red blood generating machine.'  But, I now have hemoblobin which is so near the upper limit that I may not be able to make these donations.  The little 'testor' which reads my hemablobin after a finger stick nornally registers about 17.6-17.9, and 18.0 will keep me from donating.  When I am hooked up to the machine and they do a 'real' test on my blood, the level drops to about 17.0, but the initial test is what determines whether or not I can donate.
Is there some way I can get that hemoglobin lever down, and , other than blood donations, isn't there a reason why I should?  Does this HIGH level indicate some health issue which I should address?